X-ray diagnostic apparatus

ABSTRACT

An X-ray diagnostic apparatus of an embodiment includes an image generator, a detection unit, and an irradiation control unit. The image generator successively generates X-ray images based on X-rays emitted from an X-ray tube and transmitted through a subject. The detection unit detects a position of a predetermined target included in the successively generated X-ray images. The irradiation control unit identifies, based on the detected position of the predetermined target, a region in which the predetermined target can be visualized in the X-ray images, and performs control to reduce an X-ray irradiation dose to a region other than the identified region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-159053, filed on Aug. 4, 2014; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an X-ray diagnostic apparatus.

BACKGROUND

Endovascular intervention treatment is treatment for treating an affected area in the heart, brain, liver, or other organs by inserting a treatment tool (device) called a catheter into a blood vessel. For example, in endovascular intervention treatment, a doctor inserts a balloon-tip catheter to a stricture site. The doctor then, for example, injects fluid into the balloon through the catheter and expands the balloon. The stricture site is thereby expanded to restore the blood flow. The stricture site is thereby mechanically expanded to restore the blood flow. The balloon-tip catheter is pulled out of the body by the doctor after the fluid in the balloon is sucked.

In order to prevent restenosis of the stricture site expanded by the balloon, endovascular intervention treatment is conducted using a balloon-tip catheter having a metal mesh (stent strut) affixed to the outside of the balloon. In this treatment, the doctor expands the stent strut by expanding the balloon and thereafter sucks the fluid in the balloon and pulls the catheter out of the body. The expanded stent strut is retained at the stricture site, thereby reducing the possibility of restenosis at the stricture site. The balloon-tip catheter having a stent strut is called a “stent”.

In endovascular intervention treatment, it is necessary to move the device inserted into a blood vessel precisely to a treatment target site. In general, the device is positioned with reference to an X-ray image generated and displayed real-time by an X-ray diagnostic apparatus. For this purpose, the device has, for example, x-ray-opaque metal attached at two places (or one place in some cases) as markers indicating the position of the balloon or the stent. The doctor positions the device by referring to the markers visualized in the X-ray image appearing on a monitor.

However, when endovascular intervention treatment is conducted on a blood vessel in an organ such as the heart that always pulses or an organ that moves because of pulsation, the position of the device in the X-ray image always moves. It is therefore an extremely skillful task for doctors to position the device by referring to the X-ray image.

There is conventionally known a technique for displaying moving images in which the device appears virtually stationary, for example, by tracking the markers at two points visualized in the successively generated X-ray images and deforming the images such that the markers at two points in each X-ray image are located at the same positions as in the past images. A technique as a post-process is also known, which is for highlighting the device at a high contrast, for example, by obtaining the arithmetic mean of images of a plurality of frames in which the positions of the markers at two points are corrected to be the same position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating one example of the configuration of an X-ray diagnostic apparatus according to a first embodiment;

FIG. 2 is a diagram for explaining X-ray images to be subjected to processing;

FIG. 3 is a diagram illustrating one example of the configuration of an image processor and a system controller according to the first embodiment;

FIGS. 4A and 4B are diagrams for explaining processing that a marker coordinate detection unit according to the first embodiment performs;

FIG. 5 is a diagram for explaining one example of a Learning mode according to the first embodiment;

FIGS. 6A and 6B are diagrams for explaining processing that a corrected-image generation unit according to the first embodiment performs;

FIG. 7 is a diagram for explaining one example of a Tracking mode according to the first embodiment;

FIG. 8 is a diagram for explaining one example of processing that an image post-processing unit according to the first embodiment performs;

FIGS. 9A and 9B are diagrams illustrating one example of moving images that a display controller according to the first embodiment displays;

FIG. 10, sections (A) through (C), is a diagram for explaining one example of processing that an irradiation controller according to the first embodiment performs;

FIG. 11 is a diagram for explaining one example of moving image display according to the first embodiment;

FIG. 12 is a flowchart illustrating a procedure of processing in the X-ray diagnostic apparatus according to the first embodiment;

FIG. 13, sections (A) and (B), is a diagram for explaining processing performed by an irradiation control unit and an image processing control unit according to a second embodiment;

FIG. 14 is a flowchart illustrating a procedure of processing in the X-ray diagnostic apparatus according to the second embodiment;

FIG. 15, sections (A) and (B), is a diagram for explaining one example of processing that an X-ray diagnostic apparatus according to a third embodiment performs;

FIG. 16 is a flowchart illustrating a procedure of processing in the X-ray diagnostic apparatus according to the third embodiment;

FIG. 17, sections (A) through (C), is a diagram for explaining one example of processing that an X-ray diagnostic apparatus according to a fourth embodiment performs;

FIG. 18 is a flowchart illustrating a procedure of processing in the X-ray diagnostic apparatus according to the fourth embodiment;

FIGS. 19A and 19B are diagrams for explaining an X-ray diagnostic apparatus according to a fifth embodiment;

FIG. 20 is a diagram illustrating one example of the configuration of an image processing unit according to a sixth embodiment;

FIG. 21 is a diagram for explaining X-ray images according to the sixth embodiment;

FIGS. 22A and 22B are diagrams for explaining a marker coordinate detection unit according to the sixth embodiment;

FIGS. 23A and 23B are diagrams for explaining a periodic trace data acquisition unit;

FIG. 24 is a diagram for explaining new images according to the sixth embodiment;

FIG. 25 is a diagram for explaining a corrected-image generation unit according to the sixth embodiment;

FIG. 26 is a diagram for explaining an X-ray diagnostic apparatus according to a seventh embodiment;

FIG. 27 is a diagram for explaining the X-ray diagnostic apparatus according to the seventh embodiment;

FIG. 28 is a diagram for explaining an image processing unit according to the seventh embodiment;

FIG. 29 is a diagram for explaining the image processing unit according to the seventh embodiment;

FIG. 30 is a diagram for explaining the image processing unit according to the seventh embodiment; and

FIG. 31 is a diagram for explaining the image processing unit according to the seventh embodiment.

DETAILED DESCRIPTION

According to an embodiment, an X-ray diagnostic apparatus includes processing circuitry. The processing circuitry configured to successively generate X-ray images based on X-rays emitted from an X-ray tube and transmitted through a subject. The processing circuitry configured to detect a position of a predetermined target included in the successively generated X-ray images, based on the position of the predetermined target, identify a region in which the predetermined target is capable of being visualized in the X-ray images. The processing circuitry configured to perform control to reduce an X-ray irradiation dose to a region other than the identified region.

The following describes embodiments of X-ray diagnostic apparatuses in detail with reference to the accompanying drawings.

First Embodiment

First, the overall configuration of an X-ray diagnostic apparatus according to a first embodiment is described. FIG. 1 is a diagram illustrating one example of the configuration of an X-ray diagnostic apparatus 100 according to the first embodiment. As illustrated in FIG. 1, the X-ray diagnostic apparatus 100 according to the first embodiment includes a high voltage generator 11, an X-ray tube 12, an X-ray collimator device 13, a table 14, a C-arm 15, an X-ray detector 16, a C-arm rotating/moving mechanism 17, a table moving mechanism 18, a C-arm/table mechanism controller 19, a collimator controller 20, a system controller 21, an input unit 22, a display unit 23, an image data generator 24, an image data storage unit 25, and an image processor 26.

Functions, described below, of the above described units are each constructed as a computer program, and implemented by a circuit executing the computer program. For example, processing functions to be performed by the C-arm/table mechanism controller 19, the collimator controller 20, the system controller 21, the image data generator 24, and the image processor 26 are stored in computer-executable forms in the image data storage unit 25 (also referred to as image data storage circuitry) or storage circuitry that is not illustrated. Circuitry reads out corresponding computer programs from the image data storage unit 25 or the storage circuitry (not illustrated), and executes the computer programs, thereby implementing functions corresponding to the respective programs.

Here, a single circuit or a plurality of circuits may be used as a circuit or circuits to execute each of the functions. More specifically, a single circuit may read out a computer program corresponding to each of the functions and implement a corresponding function, or alternatively, a plurality of circuits may read out computer programs corresponding to different functions and implement corresponding functions. Each of the above-described circuits is a processor that reads out a computer program from the image data storage unit 25 or the storage circuitry (not illustrated) and executes the computer program to implement a function corresponding to the computer program.

The term “processor” used in the above explanation refers to, for example, a circuit such as a central processing unit (CPU), a graphics processing unit (GPU), or an application specific integrated circuit (ASIC), a programmable logic device (for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), or a field programmable gate array (FPGA)). The processor reads out a computer program stored in a storage circuit and executes the computer program to implement a function. Storing a computer program in the storage circuit may be changed to embedding the computer program directly in a circuit of the processor. In this case, the processor reads the computer program embedded in the circuit and executes the computer program to implement the function. Each processor of this embodiment is not limited to a processor constructed of a single circuit, and may be constructed as a single processor having a plurality of independent circuits combined therein to implement an intended function.

The high voltage generator 11 is a device that generates high voltage and supplies the generated high voltage to the X-ray tube 12. The X-ray tube 12 is a device that generates X-rays using the high voltage supplied from the high voltage generator 11. The high voltage generator 11 adjusts the X-ray dose applied to a subject P and controls ON/OFF of X-ray irradiation on the subject P by adjusting the voltage supplied to the X-ray tube 12. The X-ray collimator device 13 is a device for narrowing X-rays generated by the X-ray tube 12 such that the X-rays are selectively applied to a region of interest of the subject P by shielding the X-rays are applied to a region other than the region of interest. For example, the X-ray collimator device 13 has four slidable collimator blades, and the collimator blades are slid to narrow X-rays generated by the X-ray tube 12 and apply the narrowed X-rays to the subject P.

The table 14 is a bed on which the subject P lies, and is disposed on a couch (not illustrated). The X-ray detector 16 detects X-rays transmitted through the subject P. For example, the X-ray detector 16 has detection elements arranged in a matrix. Each detection element converts X-rays transmitted through the subject P into an electrical signal, accumulates the thus converted electrical signals, and transmits the accumulated electrical signals to the image data generator 24 described later. The C-arm 15 is an arm for holding the X-ray tube 12, the X-ray collimator device 13, and the X-ray detector 16. “The X-ray tube 12 and the X-ray collimator device 13” and the X-ray detector 16 are disposed so as to be opposed to each other by the C-arm 15 with the subject P placed therebetween.

The C-arm rotating/moving mechanism 17 is a mechanism for rotating and moving the C-arm 15. The C-arm rotating/moving mechanism 17 can change a source image receptor distance (SID) that is the distance between the X-ray tube 12 and the X-ray detector 16. The C-arm rotating/moving mechanism 17 can also rotate the X-ray detector 16 held by the C-arm 15. The table moving mechanism 18 is a mechanism for moving the table 14. The C-arm/table mechanism controller 19 adjusts the rotation and movement of the C-arm 15 and the movement of the table 14 by controlling the C-arm rotating/moving mechanism 17 and the table moving mechanism 18 under the control of the system controller 21 described later. The C-arm/table mechanism controller 19 is also referred to as C-arm/table mechanism control circuitry, and reads out a computer program corresponding to the above-described C-arm/table mechanism controlling function from the image data storage unit 25 or the storage circuitry (not illustrated), and executes the computer program. The collimator controller 20 controls an irradiation range of X-rays applied to the subject P by adjusting the aperture of the collimator blades of the X-ray collimator device 13 under the control of the system controller 21 described later. The collimator controller 20 is also referred to as collimator control circuitry, and reads out a computer program corresponding to the above-described collimator controlling function from the image data storage unit 25 or the storage circuitry (not illustrated), and executes the computer program.

The image data generator 24 generates X-ray images based on X-rays emitted from the X-ray tube 12 and transmitted through the subject. Specifically, the image data generator 24 generates X-ray images by use of the electrical signals converted from X-rays by the X-ray detector 16 and stores the generated X-ray images into the image data storage unit 25. For example, the image data generator 24 performs current/voltage conversion, A (analog)/D (digital) conversion, and parallel/serial conversion on the electrical signals received from the X-ray detector 16 and generates image data. The image data generator 24 is also referred to as image data generation circuitry, and reads out a computer program corresponding to the above-described image data generating function from the image data storage unit 25 or the storage circuitry (not illustrated), and executes the computer program.

The image data storage unit 25 stores therein X-ray images generated by the image data generator 24. The image data storage unit 25 is also referred to as image data storage circuitry, and stores therein, for example, computer programs corresponding to the respective functions. The image processor 26 is a processor that executes a variety of image processing on X-ray images stored in the image data storage unit 25. Specifically, the image processor 26 executes a variety of image processing on X-ray images generated by the image data generator 24. For example, the image processor 26 acquires an X-ray image directly from the image data generator 24 and performs a variety of image processing thereon. Otherwise, for example, the image processor 26 acquires an X-ray image generated by the image data generator 24 from the image data storage unit 25 and performs a variety of image processing thereon. The image processor 26 can also store image data subjected to image processing into the image storage unit 25. The image processor 26 is also referred to as image processing circuitry, and reads out a computer program corresponding to the above-described image processing function from the image data storage unit 25 and executes the computer program.

The input unit 22 is a control unit to be used by an operator (for example, a doctor or a technician) to operate the X-ray diagnostic apparatus, and accepts a variety of instructions from the operator. For example, the input unit 22 includes a mouse, a keyboard, a button, a trackball, a joystick, and a footswitch. The input unit 22 transfers the instructions accepted from the operator to the system controller 21 described later. The input unit 22 is also referred to as input circuitry.

The display unit 23 has a monitor for displaying a graphical user interface (GUI) for accepting a command from the operator through the input unit 22 and for displaying X-ray images generated by the image data generator 24, X-ray images subjected to image processing by the image processor 26, and other images. The display unit 23 may display image data output by the image data generator 24 or the image processor 26 or may display image data acquired from the image data storage unit 25. The display unit 23 is also referred to as a display.

The system controller 21 controls the entire operation of the X-ray diagnostic apparatus 100. More specifically, the system controller 21 controls the high voltage generator 11, the C-arm/table mechanism controller 19, and the collimator controller 20 in accordance with a command from the operator that has been transferred from the input unit 22. The system controller 21 thus adjusts the X-ray dose, controls ON/OFF of X-ray irradiation, adjusts rotation and movement of the C-arm 15, and adjusts movement of the table 14. Additionally, the system controller 21 defines a certain region of interest on image data generated by the image data generator 24, and, based on a result of comparison between an average pixel value of the defined region of interest and a predetermined threshold, executes automatic brightness control (ABC).

Furthermore, the system controller 21 performs control over image generation processing in the image data generator 24 and image processing in the image processor 26 described below, in accordance with commands from the operator. The system controller 21 also performs control so that the GUI for accepting a command from an operator, X-ray images stored in the image data storage unit 25, and X-ray images subjected to image processing by the image processor 26 can be displayed on a monitor of the display unit 23. The system controller 21 is also referred to as system control circuitry, and reads out a computer program corresponding to the above-described system controlling function from the image data storage unit 25 or the storage circuitry (not illustrated), and executes the computer program.

The overall configuration of the X-ray diagnostic apparatus 100 is as described above. This configuration enables the X-ray diagnostic apparatus 100 according to the first embodiment to reduce radiation exposure. Specifically, the X-ray diagnostic apparatus 100 is enabled to display, with reduced radiation exposure, X-ray images for which the visibility of a treatment tool (device) displayed therein is ensured during execution of endovascular intervention treatment performed with reference to the X-ray images.

For example, when conducting endovascular intervention treatment using a “balloon-tip catheter having a stent strut” for a stricture site in a blood vessel in the heart of the subject P, a doctor positions the device with reference to X-ray images generated by the X-ray diagnostic apparatus. As described above, when endovascular intervention treatment is conducted on a blood vessel in an organ such as the heart that always pulses or in an organ that moves because of pulsation, the position of the device in X-ray images moves. It is therefore an extremely skillful task for doctors to position the device by referring to X-ray images.

In a conventional technique, moving images are displayed in which the device appears virtually stationary. Such display is enabled, for example, by tracking markers at two points visualized in the sequentially generated X-ray images and deforming the images such that the markers at two points in each X-ray image are located at the same positions as in the past images. For example, as illustrated in FIG. 2, the X-ray tube 12 emits X-rays to a region of interest (for example, the heart) of the subject P, and the X-ray detector 16 sequentially detects X-rays transmitted through the region of interest. The X-ray diagnostic apparatus 100 performs image processing based on data successively detected by the X-ray detector 16 such that a device contained in X-ray images sequentially generated in a time-series manner appears virtually stationary. The X-ray diagnostic apparatus 100 displays these X-ray images as moving images on a real-time basis. FIG. 2 is a diagram for explaining X-ray images to be subjected to the processing.

This processing enables the X-ray diagnostic apparatus 100 to display X-ray images for which the visibility of a device displayed therein is ensured during execution of endovascular intervention treatment performed with reference to the X-ray images, thereby enabling the X-ray diagnostic apparatus 100 to facilitate the positioning of the device. With the above-described technique, however, it may increase radiation exposure due to the character of the manipulation. In order to avoid this inconvenience, the X-ray diagnostic apparatus 100 according to the present application uses the system controller 21 detailed hereinafter to allow for reduced radiation exposure for displaying moving images in which the device appears virtually stationary.

Here, the following firstly describes processing that the image processor 26 performs for displaying moving images in which the device appears virtually stationary, and then describes control to be performed by the system controller 21 according to this embodiment. FIG. 3 is a diagram illustrating one example of the configuration of the image processor 26 and the system controller 21 according to the first embodiment. As illustrated in FIG. 3, the image processor 26 includes a marker coordinate detection unit 26 a, a corrected-image generation unit 26 b, and an image post-processing unit 26 c. More specifically, image processing circuitry, which executes the image processing function, reads out computer programs corresponding to functions of the marker coordinate detection unit 26 a, the corrected-image generation unit 26 b, and the image post-processing unit 26 c from the image data storage unit 25 or the storage unit (not illustrated). The image processing circuitry then executes the computer programs, thereby executing functions described below.

The marker coordinate detection unit 26 a localizes a predetermined target regarding a medical device inserted into the body of a subject by use of a cluster of X-ray images sequentially generated by the image data generator 24 within a predetermined period, and detects, based on the localization result, the positions of the predetermined target in newly generated X-ray images. Specifically, each time a new image, which is a new X-ray image, is stored into the image data storage unit 25, the marker coordinate detection unit 26 a detects coordinate points of stent markers attached to a stent or a coordinate point of one point depending on the stent markers (for example, the midpoint therebetween) in the new image. For example, based on information on the stent markers visualized in images, the marker coordinate detection unit 26 a detects the positions of the stent markers in sequentially generated X-ray images. In one illustrative example, based on information on stent markers designated by an operator or on a teacher image of the stent markers, the marker coordinate detection unit 26 a detects the positions of the stent markers or the position of one point depending on the stent markers (for example, the midpoint therebetween) in sequentially generated X-ray images.

The following describes an example of the case where positions of two stent markers are detected. FIGS. 4A and 4B are diagrams for explaining processing that the marker coordinate detection unit 26 a according to the first embodiment performs. For example, as illustrated in FIG. 4A, the system controller 21 described below performs control such that an X-ray image (a first frame) stored in the image data storage unit 25 appears on a monitor of the display unit 23. An operator (such as a doctor), referring to the first frame, designates two stent markers in the first frame via the input unit 22, as illustrated in FIG. 4A. The marker coordinate detection unit 26 a thus detects a coordinate point of each of the two stent markers in the first frame.

As illustrated in FIG. 4A, the marker coordinate detection unit 26 a then defines, as a region of interest (ROI), a rectangle centering on a coordinate point of each of the two stent markers designated in the first frame, and extracts patterns that resemble a pattern in each of the defined ROIs from each of the sequentially generated new images, for example, by a cross-correlation method. The marker coordinate detection unit 26 a detects, as a coordinate point of the stent marker, a coordinate point that has the highest cross-correlation value.

FIG. 4A illustrates a case where an operator designates two locations of stent markers. However, this embodiment is not limited to this case, and may include a case where an operator designates one location of a stent marker. In such a case, the marker coordinate detection unit 26 a detects a coordinate point of the other stent marker even in the first frame by executing the cross-correlation method using an ROI defined based on a coordinate point of the designated stent marker.

Alternatively, the marker coordinate detection unit 26 a uses a teacher image to detect a coordinate point of a stent marker. The teacher image represents shape and brightness characteristics to be exhibited in an X-ray image by a stent marker attached to a stent that is actually used in medical treatment. For example, as illustrated in FIG. 4B, with an X-ray image of a stent marker previously stored separately as a teacher image, the marker coordinate detection unit 26 a extracts patterns resembling the teacher image from each new image, and searches for a region with the highest resemblance from the thus extracted candidate regions of the stent marker, thereby detecting the coordinate point of the stent marker.

Here, when detecting coordinate points of the stent marker from sequentially generated X-ray images, the marker coordinate detection unit 26 a identifies (localizes) the stent marker by using a plurality of X-ray images. More specifically, using a cluster of X-ray images sequentially generated by the image data generator 24 within a predetermined period, the marker coordinate detection unit 26 a localizes a predetermined target inserted into the body of a subject and visualized in X-ray images. Based on the localization result, the marker coordinate detection unit 26 a then detects the positions of the predetermined target contained in newly generated X-ray images. For example, using a stent marker that has been designated by an operator or that is based on a teacher image, the marker coordinate detection unit 26 a extracts, from each of a plurality of X-ray images within a predetermined period, all regions that resemble the stent marker. The marker coordinate detection unit 26 a then extracts, as the stent marker, a region that is the most similar to the stent marker from the regions extracted from each of the X-ray images. In the following description, the above-described processing for detecting and identifying (localizing) a stent marker is referred to as a “Learning mode”.

FIG. 5 is a diagram for explaining one example of the Learning mode according to the first embodiment. FIG. 5 illustrates the Learning mode where X-ray images corresponding to n frames are used, which have been generated by the image data generator 24. For example, the marker coordinate detection unit 26 a extracts all regions (coordinate points) resembling a stent marker from the entire region of the first frame illustrated in FIG. 5. The marker coordinate detection unit 26 a pairs each of all of the extracted coordinate points with each of the other ones thereof, and assigns a score to each of the pairs in accordance with such a factor as resemblance. For example, the marker coordinate detection unit 26 a assigns a score to a pair of a coordinate point 51 and another coordinate point 52. Although FIG. 5 illustrates only the coordinate point 51 and the coordinate point 52, any other region (coordinate point) resembling the stent marker contained therein is detected and is paired with the coordinate point 51, with the coordinate point 52, and with any other coordinate point. Scores are then assigned to those pairs.

Likewise, the marker coordinate detection unit 26 a performs the above-described processing with respect to each of the second to n-th frames, thereby assigning scores to individual pairs determined based on all of extracted coordinate points. The marker coordinate detection unit 26 a then extracts, as the coordinate points of the stent markers, the coordinate points that give the highest score for each frame, and then extracts a region where the stent marker may be located in X-ray images in the predetermined period. For example, as illustrated in FIG. 5, the marker coordinate detection unit 26 a extracts pairs of coordinate points 51 and coordinate points 52 that give the highest scores in the respective frames, and then extracts a region R1 where these coordinate points are included. The extraction of the region R1 is performed, for example, in such a manner that, after rectangles of a predetermined size each centering on the midpoint between the corresponding coordinate point 51 and the corresponding coordinate point 52 are extracted from the respective frames, a region that includes all of the extracted rectangles is extracted as the region R1.

For example, such movements as heartbeats and lung expansion/contraction continue in an orderly (periodic) manner, so that a stent marker, which moves following such movements, appears to move in an orderly (periodic) manner. In the above-described Learning mode, stent markers appearing to move in orderly manners (periodically) are exhaustively detected by use of the X-ray images within the predetermined period, one of those stent markers that resembles the stent marker most is identified (localized) as the stent marker. In the Learning mode, for example, X-ray images corresponding to around 40 frames are used.

As described above, the marker coordinate detection unit 26 a performs the Learning mode, so that it identifies (localizes) the stent marker in the X-ray images and extracts a region including positions where the stent marker may be located. The marker coordinate detection unit 26 a then sets the extracted region as the target region, and detects the stent marker from the target region. For example, the marker coordinate detection unit 26 a sets the region R1 illustrated in FIG. 5 as the target region of the processing, and performs processing for detecting therefrom the stent marker in newly generated X-ray images.

Back to FIG. 3, the corrected-image generation unit 26 b sets, as reference coordinate points, the coordinate point of the stent marker that has already been detected by the marker coordinate detection unit 26 a. The corrected-image generation unit 26 b generates corrected images by performing image displacement such as translation and rotation, and image deformation such as affine transform on new images so that the coordinate points of the stent marker that have been detected by the marker coordinate detection unit 26 a in the new images can be the same coordinate points as the reference coordinate point. FIGS. 6A and 6B are diagrams for explaining processing that the corrected-image generation unit 26 b according to the first embodiment performs. FIGS. 6A and 6B illustrate processing on a new image from which the coordinate point of the stent marker has been detected based on the processing result of the Learning mode after the marker coordinate detection unit 26 a has completed the processing of the Learning mode. More specifically, the first frame illustrated in FIGS. 6A and 6B refers to an X-ray image generated first after the completion of the Learning mode.

For example, the marker coordinate detection unit 26 a first executes the processing of Learning mode by using images corresponding to 40 frames. As illustrated in FIG. 6A, the marker coordinate detection unit 26 a then detects the coordinate points of the stent marker from the first frame and the second frame that have been generated after the completion of the Learning mode, by using the processing result of the Learning mode. When the marker coordinate detection unit 26 a has detected the coordinate points of the stent marker, as illustrated in FIG. 6A, the corrected-image generation unit 26 b generates a corrected image 2 from the second frame through image deformation so that the coordinate point of the stent marker, detected in an X-ray image corresponding to the second frame generated as a new image, can be the same as the coordinate point (reference position) of the stent marker that has been already detected in the first frame. The corrected-image generation unit 26 b then generates a corrected image with respect to a new image corresponding to each of the third and subsequent frames by using, as the reference position (reference coordinate point), the coordinate point of the stent marker in a corrected image generated by the corrected-image generation unit 26 b from an X-ray image generated immediately before the new image. For example, as illustrated in FIG. 6B, the corrected-image generation unit 26 b generates a corrected image 3 from the third frame by performing image deformation such that the coordinate point of the stent marker detected from the third frame can be the same as the coordinate point of the stent marker in the corrected image 2 generated from the second frame.

In the above description, the embodiment is configured such that the coordinate point of the stent marker in a corrected image generated from a frame immediately before a new image is used as the reference coordinate point. Embodiments are not limited to this configuration, and may be configured such that corrected images from new images corresponding to the second and subsequent frames are generated while the coordinate point of the stent marker detected in the first frame is constantly used as the reference coordinate point. However, as described below, corrected images are used for generating images to be displayed in display of moving images. To reliably execute display of moving images in which the position of the stent marker is invariable, it is therefore desirable that a corrected image be generated from a new image by use of an immediately preceding corrected image.

As described above, the corrected-image generation unit 26 b generates corrected images in which the coordinate points of the stent marker detected by the marker coordinate detection unit 26 a are set to the same coordinate point. More specifically, after the stent marker is identified through the Learning mode, the corrected-image generation unit 26 b generates corrected images in which the coordinate points of the stent marker detected from succeeding X-ray images are set to the same coordinate point, by using the processing result of the Learning mode. In the following description, the above-described processing to generate corrected images is referred to as a “Tracking mode”.

FIG. 7 is a diagram for explaining one example of the Tracking mode according to the first embodiment. For example, in the Tracking mode, as illustrated in FIG. 7, corrected images are generated through image deformation such that the positions of a stent marker detected within the region R1 extracted through the Learning mode are set at the same position. More specifically, the corrected-image generation unit 26 b generates corrected images for X-ray images from which the stent marker is detected by the marker coordinate detection unit 26 a after the Learning mode.

Back to FIG. 3, the image post-processing unit 26 c performs post-processing on corrected images generated by the corrected-image generation unit 26 b. FIG. 8 is a diagram for explaining one example of processing that the image post-processing unit 26 c according to the first embodiment performs. For example, as illustrated in FIG. 8, the image post-processing unit 26 c generates a filtered corrected image by executing high-frequency noise reduction filtering and low-frequency component removal filtering on a corrected image having the stent marker at the same position as the first frame. The image post-processing unit 26 c further generates a logarithmic image by calculating natural logarithmic values of the pixel values of the respective pixels included in the filtered corrected image. The image post-processing unit 26 c executes the above-described post-processing also with respect to the first frame.

Here, the image post-processing unit 26 c performs high-frequency noise reduction processing using a spatial filter that is described, for example, in the following documents: K. Nambu, H. Iseki, “A noise reduction method based on a statistical test of high dimensional pixel vectors for dynamic and volumetric images”, Riv Neuroradiol 2005, 18:21-33; and Nishiki, “Method for reducing noise in X-ray images by averaging pixels based on the normalized difference with the relevant pixel”, Radiological Physics and Technology, Vol. 2, 2008.

This spatial filter applies high-frequency noise reduction processing in which: differences in pixel value between frames of different points in time are measured; while different weights are assigned according to the magnitudes of the differences, smoothening is performed within a single frame. This filter can reduce high-frequency noise without affecting other frames. Here, because corrected images have the stent marker located at the same coordinate point, the spatial filter can be applied exhaustively, thereby reducing high-frequency noise in a portion corresponding to the stent and allowing for enhanced visibility of the stent in the corrected images.

Alternatively, the image post-processing unit 26 c may execute high-frequency noise reduction filtering using, for example, a recursive filter is applied. A recursive filter is a filter that reduces high-frequency noise by adding, to pixel values of the pixels included in a frame to be filtered, pixel values of the pixels included in a past frame to which predetermined weights are assigned. Because corrected images have the stent marker at the same coordinate point, a recursive filter, where a past frame is used for the filtering, also reduces high-frequency noise in a portion corresponding to the stent, thereby allowing for enhanced visibility of the stent in the corrected images.

The image post-processing unit 26 c performs low-frequency component removal filtering with a high-pass filter. The contrast thus can be reduced in a background portion in each of the corrected images, which is a portion other than the stent portion. The image post-processing unit 26 c further performs processing to generate a logarithmic image on a filtered corrected image, thereby allowing each component of a signal to be constant throughout an image.

The description of processing that the image processor 26 performs when displaying moving images in which the device appears virtually stationary ends here. The following describes the system controller 21 according to the first embodiment. As illustrated in FIG. 3, the system controller 21 includes an irradiation control unit 21 a, an image processing control unit 21 b, and a display control unit 21 c. More specifically, system control circuitry, which executes the system controlling function, reads out computer programs corresponding to functions of the irradiation control unit 21 a, the image processing control unit 21 b, and the display control unit 21 c from the image data storage unit 25 or the storage unit (not illustrated). The image processing circuitry then executes the computer programs, thereby executing functions described below. Here, the irradiation control unit 21 a and the image processing control unit 21 b reduce radiation exposure for displaying moving images in which the device appears virtually stationary, details of this processing are described after the following description.

Each time the image post-processing unit 26 c newly generates a logarithmic image in a time-series manner, the display control unit 21 c performs control to sequentially display the newly generated logarithmic image, as an image to be displayed, on the monitor of the display unit 23. More specifically, the display control unit 21 c performs control to display, as moving images, images to be displayed (stent-fixed images) in which the coordinate points of the stent marker are located at the same position. Although the background portion other than the stent portion is blurred as a result, X-ray images can be displayed as moving images with the stent portion appearing stationary.

Here, the display control unit 21 c displays the stent-fixed images in any one of various forms according to a display-form instruction command received from an operator via the input unit 22. Specifically, the display control unit 21 c performs control, according to the display-form instruction command, to display defined regions as the stent-fixed images. The defined regions are determined based on the coordinate points of the stent marker in the logarithmic images. For example, when the coordinate points of two stent markers in a logarithmic image are (X1, Y1) and (X2, Y2), the display control unit 21 c sets up, as the defined region, a rectangular region centering on ((X1+X2)/2, (Y1+Y2)/2) and having a width of “2×|X1-X2|” and a height of “2×|Y1-Y2|”. The display control unit 21 c then performs control to display the logarithmic image while masking a region thereof other than the defined region.

The display control unit 21 c performs control to display enlarged images obtained by enlarging the defined regions as the stent-fixed images. Here, when the stent-fixed images only of one kind, i.e., the logarithmic images, the defined regions, or the enlarged images, are exclusively displayed, the display control unit 21 c performs control to put the positions of the stent marker in these stent-fixed images at the center of the monitor of the display unit 23. Alternatively, the display control unit 21 c performs control according to the display-form instruction command so that original images of images to be displayed may be displayed in parallel with the stent-fixed images. Here, when these images are displayed in parallel, if the defined regions or the enlarged images are stent-fixed images, the display control unit 21 c performs control to display, as original images, regions corresponding to the defined regions.

FIGS. 9A and 9B are diagrams illustrating one example of moving images that the display control unit 21 c according to the first embodiment displays. For example, as illustrated in FIG. 9A, the display control unit 21 c performs control to display original images as moving images and the defined regions as moving images in parallel on the monitor of the display unit 23. The original images have boundaries added thereon that correspond to the defined regions. Otherwise, as illustrated in FIG. 9B, the display control unit 21 c performs control to display original images as moving images and the enlarged images as moving images in parallel on the monitor of the display unit 23. The original images have boundaries added thereon that correspond to the defined regions.

Here, in each of the defined regions and each of the enlarged images, as illustrated in FIGS. 9A and 9B, the stent strut appears more clearly, and the contrast in the background portion is weaker, than in original images thereof as a result of the above-described post-processing. The entire stent is thus more visible. The boundaries on such original images move following the move of the position of stent marker. The original images and the stent-fixed images may be displayed in parallel as described above on one monitor included in the display unit 23. Alternatively, the display unit 23 that includes a plurality of monitors may display each of the original images and each of the stent-fixed images on two different monitors.

Described above is a case where this embodiment is configured to set logarithmic images, defined region, or enlarged images as stent-fixed images. However, this embodiment is not limited to this case, However, this embodiment is not limited to this case, and may be such that the corrected images as they are, or images subjected to a desirable combination of two or more kinds of post-processing selected from high-frequency noise reduction filtering, low-frequency component removal filtering, and logarithmic-image generation processing are used as images to be displayed, which has been set by an operator.

As described above, the X-ray diagnostic apparatus 100 identifies a stent marker through the Learning mode with a plurality of X-ray images, and detects the stent marker in succeeding X-ray images on the basis of the identification result. The X-ray diagnostic apparatus 100 then generates stent-fixed images through the Tracking mode and displays the stent-fixed images as moving images. The irradiation control unit 21 a and the image processing control unit 21 b enable reduction in radiation exposure in display of moving images of stent-fixed images. The radiation exposure reduction processing including control performed by the image processing control unit 21 b is explained in detail in the second embodiment.

Specifically, the irradiation control unit 21 a identifies the region where the stent marker may be visualized in the X-ray images, based on the positions of the predetermined target (stent marker) detected by the marker coordinate detection unit 26 a, and performs control to reduce an X-ray irradiation dose for the position corresponding to a region other than the identified region. Specifically, the irradiation control unit 21 a performs control to apply low dose to a region corresponding to a region that does not include the stent marker (stent) in X-ray images generated by the image data generator 24 in a time-series manner. For example, the irradiation control unit 21 a inserts the X-ray collimator to shield X-rays into a region that does not include the stent marker, or inserts an X-ray absorption filter to attenuate X-rays.

FIG. 10 is a diagram for explaining processing performed by the irradiation control unit 21 a according to the first embodiment. For example, as illustrated in (A) of FIG. 10, a stent marker, which moves following movements such as heartbeats and lung expansion and contraction, appears to move in an orderly manner in X-ray images. Specifically, the stent marker in a plurality of X-ray images collected in time series repeatedly exhibits periodically reciprocating movement between similar positions. When stent-fixed images are displayed, it is important for the operator such as a doctor to clearly observe the region around the stent, and it is not very important to observe positions distant from the stent.

For this reason, as illustrated in (B) of FIG. 10, the irradiation control unit 21 a identifies a region R2 including the stent marker in each of the X-ray images, and reduces an X-ray irradiation dose to a region R3 that is different from the identified R2, to reduce radiation exposure. The irradiation control unit 21 a can identify the region R2 by acquiring coordinate information of a processing result in the Learning mode from the marker coordinate detection unit 26 a. Otherwise, the irradiation control unit 21 a can identify the region R2 by acquiring coordinate information of the detection result from the marker coordinate detection unit 26 a after the Learning mode is finished.

After identifying the region R2, the irradiation control unit 21 a extracts region R3 in each X-ray image using the identified region R2, and reduces the X-ray irradiation dose to the region of the subject corresponding to the extracted region R3. For example, the irradiation control unit 21 a controls the X-ray collimator device 13 via the collimator controller 20, to apply X-rays to the region R2. Otherwise, the irradiation control unit 21 a reduces the X-ray irradiation dose by inserting an X-ray absorption filter into a position located between the X-ray tube 12 and the subject P and corresponding to the region R3, to attenuate the X-rays applied to the position of the subject corresponding to the region R3.

The above control for the X-ray collimator device 13 and the X-ray absorption filter is required to be performed in real time in parallel with irradiation of X-rays to generate the X-ray images. For this reason, when the region R3 changes little by little between the X-ray images as illustrated in (B) of FIG. 10, the irradiation control unit 21 a predicts change of the region R3 in advance based on the processing result in the Learning mode, and controls the X-ray collimator device 13 and the X-ray absorption filter in accordance with the predicted change.

However, because the above control requires fine control, a region R4 including all the regions R2 may be calculated, to control irradiation of X-rays for a region R5 that is not included in the calculated region R4, as illustrated in (C) of FIG. 10. In such a case, the irradiation control unit 21 a identifies a region in which the stent marker can be visualized in each of the X-ray images, based on the positions of the stent marker detected from a plurality of X-ray images by the marker coordinate detection unit 26 a, and performs control to reduce the X-ray irradiation dose for the position corresponding to a region different from the region that includes all the identified regions.

Specifically, the irradiation control unit 21 a calculates the region R4 by adding regions necessary for displaying the stent with the movement of the stent virtually stopped, and then controls the X-ray collimator device 13 and the X-ray adsorption filter to reduce X-rays in the position corresponding to the region R5 that is different from the region R4. With this structure, control of the X-ray collimator device 13 and the X-ray absorption filter is needed to be performed only one time initially, and radiation exposure can be easy reduced.

FIG. 11 is a diagram for explaining an example of moving image display according to the first embodiment. FIG. 11 illustrates moving image display of original images and stent-fixed images generated by control performed by the irradiation control unit 21 a. As illustrated in FIG. 11, clear images are displayed as the stent-fixed images. By contrast, no images or images that are difficult to observe are displayed in the region R5 in the original images, while images that are easy to observe are displayed in the region R4.

The following describes a procedure of processing in the X-ray diagnostic apparatus 100 with reference to FIG. 12. FIG. 12 is a flowchart illustrating a procedure of processing in the X-ray diagnostic apparatus 100 according to the first embodiment. The following procedure of processing is illustrated as applying to a case where a stent marker is identified and detected as a predetermined target. As illustrated in FIG. 12, in the X-ray diagnostic apparatus 100 according to the first embodiment, when fluoroscopy is started (Yes at Step S101), the marker coordinate detection unit 26 a identifies the stent marker through the Learning mode (Step S102).

The irradiation control unit 21 a calculates a region including the identified stent marker (Step S103), and performs control to reduce the dose in the region other than the calculated region (Step S104). When the marker coordinate detection unit 26 a thereafter detects, based on the identification result, the stent marker in new X-ray images, the corrected-image generation unit 26 b generates stent-fixed images through the Tracking mode (Step S105), and the display control unit 21 c displays the stent-fixed images on the display unit (Step S106).

Thereafter, the X-ray diagnostic apparatus 100 determines whether an ending request has been input (Step S107). If the ending request has not been input at this step (No at Step S107), the display control unit 21 c continues display of the stent-fixed images. By contrast, if the ending request has been input (Yes at Step S107), the X-ray diagnostic apparatus 100 ends the processing.

Although the processing illustrated in FIG. 12 illustrates an example in which control is performed to reduce the dose to the region other than the region including the stent marker, and then the stent-fixed images are generated and displayed, the embodiment is not limited to this example. For example, the processing may be ended after control is performed to reduce the dose. In such a case, for example, generation and display of the stent-fixed images may be controlled through a stent-fixed image display mode. As an example, in step S104 in FIG. 12, after control is performed to reduce the dose to the region other than the region including the stent marker, the corrected-image generation unit 26 b determines whether the stent-fixed image display mode is ON. When the stent-fixed image display mode is ON, the corrected-image generation unit 26 b generates stent-fixed images, and the display control unit 21 c displays the stent-fixed images on the display unit 23. By contrast, when the stent-fixed image display mode is OFF, the X-ray diagnostic apparatus 100 ends the processing. The X-ray diagnostic apparatus 100 may receive an operation to turn on the stent-fixed image display mode while performing control to reduce the dose to the region other than the region including the stent marker, and thereafter perform control to generate and display stent-fixed images.

As described above, according to the first embodiment, the image data generator 24 successively generates X-ray images based on X-rays emitted from the X-ray tube 12 and transmitted through the subject. The marker coordinate detection unit 26 a detects positions of the predetermined target (stent marker) included in the X-ray images successively generated by the image data generator 24. The corrected-image generation unit 26 b successively generates corrected images obtained by subjecting newly generated X-ray images to correction processing to cause the positions of the stent marker detected in the newly generated X-ray images to coincide with a reference position. The reference position is the position of the stent marker that is detected in a reference image set as a predetermined X-ray image. The irradiation control unit 21 a identifies, based on the positions of the stent marker detected by the marker coordinate detection unit 26 a, the region in which the predetermined target can be visualized in the X-ray images, and performs control to reduce the X-ray irradiation dose for the position corresponding to the region different from the identified region. The display control unit 21 c displays on the display unit 23, as moving images, the corrected images that are successively generated by the corrected-image generation unit 26 b. With this structure, the X-ray diagnostic apparatus 100 according to the first embodiment enables reduction in X-ray dose to the region other than the region necessary for displaying stent-fixed images, and reduction in radiation exposure.

In addition, according to the first embodiment, the marker coordinate detection unit 26 a detects the respective positions of the stent marker in X-ray images that are successively generated by the image data generator 24 for a predetermined period. The irradiation control unit 21 a identifies, based on the positions of the stent marker detected from the respective X-ray images by the marker coordinate detection unit 26 a, regions where the stent marker can be visualized in the respective X-ray images, and performs control to reduce the X-ray irradiation dose for the position corresponding to the region that is different from the region including all the identified regions. With this structure, the X-ray diagnostic apparatus 100 according to the first embodiment enables easy reduction in radiation exposure while enabling stable display of stent-fixed images.

Second Embodiment

The above first embodiment illustrates the case of reducing the dose in the region other than the region used for displaying stent-fixed images. The second embodiment illustrates the case of reducing the dose also in the region used for displaying stent-fixed images.

In the above case, the image processing control unit 21 b controls image processing on the region identified by the irradiation control unit 21 a. Specifically, the image processing control unit 21 b performs control to subject the region for displaying stent-fixed images to various image processing to improve the image quality, to enable reduction in X-ray irradiation dose in the region. In other words, performing image processing on the region for displaying stent-fixed images enables maintaining the image quality substantially equal to the image quality before the image processing, even with the reduced dose. The following explains one example of the processing with reference to FIG. 13.

FIG. 13 is a diagram for explaining processing performed by the irradiation control unit 21 a and the image processing control unit 21 b according to the second embodiment. FIG. 13 illustrates the case where the irradiation control unit 21 a identifies the region R2. For example, as illustrated in (A) of FIG. 13, the irradiation control unit 21 a performs control to use a signal-to-noise ratio (S/N) in the identified region R2 as parameters of ABC control. More specifically, the irradiation control unit 21 a reflects the S/N of the stent marker included in the region R2 on ABC control. Because the region R2 includes the stent marker, the average pixel value thereof is higher than a predetermined threshold. For this reason, through ABC control to cause the average pixel value to match the predetermined threshold, the X-ray irradiation dose to the region corresponding to the region R2 is reduced.

The image processing control unit 21 b performs control to subject the region R2 to addition processing, super noise reduction filter (SNRF) processing in the time axis direction, and recursive filtering in combination. This processing enables improvement in image quality that has been reduced due to decrease in dose. The image processing control unit 21 b performs control to perform the above image processing on each of the original images displayed as moving images and the stent-fixed images. This structure enables further reduction in radiation exposure, with visibility maintained in both the original images displayed as moving images and the stent-fixed images, as illustrated in (B) of FIG. 13.

The following explains a procedure of processing in the X-ray diagnostic apparatus 100 with reference to FIG. 14. FIG. 14 is a flowchart illustrating a procedure of processing in the X-ray diagnostic apparatus 100 according to the second embodiment. The following procedure of processing illustrates the case of identifying and detecting the stent marker as the predetermined target. As illustrated in FIG. 14, in the X-ray diagnostic apparatus 100 according to the second embodiment, when fluoroscopy is started (Yes at Step S201), the marker coordinate detection unit 26 a identifies the stent marker through the Learning mode (Step S202).

The irradiation control unit 21 a calculates the region including the identified stent marker, and performs ABC control based on the S/N of the stent marker (Step S203). When the marker coordinate detection unit 26 a thereafter detects, based on the identified result, the stent marker in the new X-ray image, the corrected-image generation unit 26 b generates stent-fixed images through the Tracking mode (Step S204) under the control by ABC, and the image processing control unit 21 b controls the image processor 26 to perform image processing on the region including the stent marker (Step S205). When the image processing is performed, the display control unit 21 c displays the stent-fixed images on the display unit 23 (Step S206).

Thereafter, the X-ray diagnostic apparatus 100 determines whether an ending request has been input (Step S207). If the ending request has not been input (No at Step S207), the display control unit 21 c continues display of the stent-fixed images. By contrast, if the ending request has been input (Yes at Step S207), the X-ray diagnostic apparatus 100 ends the processing.

As described above, according to the second embodiment, the image processing control unit 21 b controls image processing on the region identified by the irradiation control unit 21 a. The irradiation control unit 21 a performs control to reduce the X-ray irradiation dose for the position corresponding to the region, based on the image processing on the region performed by the image processing control unit 21 b. With this structure, the X-ray diagnostic apparatus 100 according to the second embodiment enables further reduction in radiation exposure.

Third Embodiment

The first and second embodiments described above illustrate the cases of reducing radiation exposure by decreasing the X-ray irradiation dose. In the third embodiment, radiation exposure is reduced by reducing the frame rate. The X-ray diagnostic apparatus 100 according to the third embodiment is different from the first embodiment in details of control performed by the irradiation control unit 21 a. The details of the control are mainly explained hereinafter.

The irradiation control unit 21 a according to the third embodiment performs control to reduce the number of X-ray images to be generated per unit time for the period in which the amount of changes, between X-ray images, in position of the stent marker detected by the marker coordinate detection unit 26 a from the X-ray images is smaller than a predetermined threshold, when X-ray images are successively generated based on X-rays transmitted through the subject. Specifically, the irradiation control unit 21 a extracts a state “in which the state with a small amount of change in position of the stent marker continues for a certain period”, and the state “in which the period with a small amount of change in position of the stent marker occurs periodically and at similar timings”, based on the amount of change in values of the coordinate point of the stent marker and a heart rate meter.

For example, the irradiation control unit 21 a calculates the amount of change, between X-ray images, in coordinate point of the stent marker detected by the marker coordinate detection unit 26 a from the X-ray images, and, if the calculated amount of change is equal to or less than a predetermined threshold, determines the amount to be a small amount of change in position of the stent marker. Otherwise, the irradiation control unit 21 a acquires information of heartbeats from a heart rate meter attached to the subject, and determines, from the acquired heartbeat information, an amount of change at the timing at which the movement of the heart by heartbeats stops to be a small amount of change in position of the stent marker. Thereafter, the irradiation control unit 21 a performs control to reduce the frame rate for the period determined as having a small amount of change in position of the stent marker.

FIG. 15 is a diagram for explaining an example of processing performed by the X-ray diagnostic apparatus 100 according to the third embodiment. For example, the irradiation control unit 21 a identifies the period when the stent marker in the X-ray images that are repeatedly generated moves with a small amount of change, as illustrated in (A) of FIG. 15. The irradiation control unit 21 a thereafter reduces the frame rate for the period with a small amount of change, to reduce the number of times of X-ray irradiation, as illustrated in (B) of FIG. 15.

As described above, the irradiation control unit 21 a performs variable frame rate control to reduce the frame rate only for the period with a small amount of change in position of the stent marker, in X-ray images that are collected in a time-series manner. In the variable frame rate control, the irradiation control unit 21 a fixes “mAs=tube current (mA)×pulse width (S)”, and performs control to increase the tube current and shorten the pulse width.

The following explains a procedure of processing in the X-ray diagnostic apparatus 100 with reference to FIG. 16. FIG. 16 is a flowchart illustrating a procedure of processing in the X-ray diagnostic apparatus 100 according to the third embodiment. The following procedure of processing illustrates the case of identifying and detecting the stent marker as the predetermined target. As illustrated in FIG. 16, in the X-ray diagnostic apparatus 100 according to the third embodiment, if fluoroscopy has been started (Yes at Step S301), the marker coordinate detection unit 26 a identifies the stent marker through the Learning mode (Step S302).

The irradiation control unit 21 a calculates a region including the identified stent marker, and determines the period with a small amount of change in position of the stent marker (Step S303). When the marker coordinate detection unit 26 a detects, based on the result identified by the marker coordinate detection unit 26 a, the stent marker in the new X-ray images while the irradiation control unit 21 a performs control to collect X-ray images with a reduced frame rate for the period with a small amount of change, the corrected-image generation unit 26 b generates stent-fixed images through the Tracking mode (Step S304). Thereafter, the display control unit 21 c displays the stent-fixed images on the display unit 23 (Step S305).

The X-ray diagnostic apparatus 100 thereafter determines whether an ending request has been input (Step S306). If the ending request has not been input (No at Step S306), the display control unit 21 c continues display of the stent-fixed images. By contrast, if the ending request has been input (Yes at Step S306), the X-ray diagnostic apparatus 100 ends the processing.

As described above, according to the third embodiment, the irradiation control unit 21 a performs control to reduce the number of X-ray images to be generated per unit time for the period in which the amount of change, between X-ray images, in position of the stent marker detected by the marker coordinate detection unit 26 a from the X-ray images is smaller than a predetermined threshold, when X-ray images are successively generated based on X-rays transmitted through the subject. With this structure, the X-ray diagnostic apparatus 100 according to the third embodiment enables further reduction in radiation exposure.

Fourth Embodiment

Each of the above embodiments illustrates the example for reducing radiation exposure. The fourth embodiment illustrates the case of stably detecting the stent marker even when the scale of the displayed images is changed. The fourth embodiment is different from the first embodiment in details of control performed by the irradiation control unit 21 a. The details of the control are mainly explained hereinafter.

The irradiation control unit 21 a according to the fourth embodiment performs control so that the marker coordinate detection unit 26 a can detect the position of the predetermined target in accordance with the scale of the images displayed by the display unit 23. FIG. 17 is a diagram for explaining one example of processing performed by the X-ray diagnostic apparatus 100 according to the fourth embodiment. FIG. 17 illustrates the case of performing an enlargement operation on the original image displayed on the display unit 23.

For example, as illustrated in (A) of FIG. 17, when an enlargement operation to enlarge an image from the center of the image is performed on an original image R6 currently displayed, the object included in a region R7 is displayed after being enlarged to the size of the original image R6. Examples of the enlargement operation are: an operation of “Livezoom” to enlarge the image while the image is viewed; changing the field-of-view size “FOV” or the distance “SID” between the X-ray tube 12 and the X-ray detector 16; and attaching the enlargement device “MAF”.

When the enlargement operation on the region R7 is performed as illustrated in (A) of FIG. 17, a plurality of regions including the stent marker may be disposed outside the region R7, as illustrated in (B) of FIG. 17. Specifically, the stent marker may be disposed outside the detection range. As illustrated in (C) of FIG. 17, the irradiation control unit 21 a moves the positions of the C-arm 15, the couch (table), and the MAF such that the stent marker falls within the region R7. More specifically, as illustrated in (C) of FIG. 17, the irradiation control unit 21 a performs control such that the current range of the region R6 becomes equal to the range of a region R8. This control enables continuous detection of the stent marker even when the enlargement operation is performed.

The following explains a procedure of processing in the X-ray diagnostic apparatus 100. FIG. 18 is a flowchart illustrating the procedure of processing in the X-ray diagnostic apparatus 100 according to the fourth embodiment. The following procedure of processing illustrates the case of identifying and detecting the stent marker as the predetermined target. As illustrated in FIG. 18, in the X-ray diagnostic apparatus according to the fourth embodiment, if fluoroscopy has been started (Yes at Step S401), the marker coordinate detection unit 26 a identifies the stent marker through the Learning mode (Step S402).

When the marker coordinate detection unit 26 a thereafter detects, based on the identified result, the stent marker in a new X-ray image, the corrected-image generation unit 26 b generates stent-fixed images through the Tracking mode (Step S403), and the display control unit 21 c displays the stent-fixed images on the display unit 23 (Step S404). The irradiation control unit 21 a thereafter determines whether enlargement has been performed (Step S405). If enlargement has been performed (Yes at Step S405), the irradiation control unit 21 a changes the region in accordance with the enlargement (Step S406). By contrast, if enlargement has not been performed (No at Step S405), the display control unit 21 c continues display of the stent-fixed images.

Thereafter, the X-ray diagnostic apparatus 100 determines whether an ending request has been input (Step S407). When the ending request has not been input at the step (No at Step S407), the display control unit 21 c continues display of the stent-fixed images. By contrast, if the ending request has been input (Yes at Step S407), the X-ray diagnostic apparatus 100 ends the processing.

As described above, according to the fourth embodiment, the irradiation control unit 21 a performs control so that the marker coordinate detection unit 26 a can detect the position of the stent marker in accordance with the scale of the images displayed by the display unit 23. With this structure, the X-ray diagnostic apparatus 100 according to the fourth embodiment enables detection of the stent marker even when an enlargement operation is performed.

Fifth Embodiment

The above-described embodiments describe cases where a single stent is used. In endovascular intervention treatment, however, a plurality of stents may be inserted at the same time. For example, when two stents are inserted, the X-ray diagnostic apparatus 100 according to a fifth embodiment, the system controller 21 performs control described below, based on the distance between these two stents. The distance between the stents may be calculated by the marker coordinate detection unit 26 a by use of coordinate points designated via the input unit 22 by an operator (doctor) referring to the first frame (an original image). Alternatively, the distance therebetween may be calculated by use of the coordinate points of stent markers that have been detected by the marker coordinate detection unit 26 a by use of a teacher image from within the first frame.

Specifically, if the two stents are determined to be adjacent to each other because the distance therebetween is not larger than a predetermined distance (for example, not more than 50 mm) on a plane space, the system controller 21 controls the corrected-image generation unit 26 b to generate corrected images through image deformation such that a plurality of the coordinate points of the stent markers associated with the respective stents are placed at the same positions as a plurality of reference positions that correspond to the stent markers. FIGS. 19A and 19B are diagrams for explaining an X-ray diagnostic apparatus according to the fifth embodiment. For example, with stents each having one stent marker at the central part of a balloon, the corrected-image generation unit 26 b performs image deformation under the control of the system controller 21 such that, as illustrated in the upper part of FIG. 19A, the coordinate points of two stent markers detected in each new image coincide with the reference coordinate points (X1, Y1) and (X2, Y2) for the two respective stents.

For example, with stents each having two stent markers at opposite sides of a balloon, the corrected-image generation unit 26 b performs image deformation under the control of the system controller 21 such that, as illustrated in the lower part of FIG. 19A, the coordinate points of four stent markers detected in each new image coincide with the reference coordinate points (X1, Y1) and (X2, Y2), and (X3, Y3) and (X4, Y4), for the two respective stents.

By contrast, if the two stents are determined to be away from each other because the distance therebetween is larger than a predetermined distance (for example, more than 50 mm) on a plane in the actual space, excessive image deformation needs to be performed in order that positions of the two respective stents coincide with corresponding positions on one image. To eliminate the need to perform excessive image deformation, as illustrated in FIG. 19B, the system controller 21 controls the image processor 26 to separately perform processing on the two respective stents (a stent 1 and a stent 2) when the two stents are away from each other. For example, the system controller 21 controls the image processor 26 to generate images to be displayed of two kinds in order that a moving image display of stent-fixed images in which the positions of the stent 1 coincide with each other, and a moving image display of stent-fixed images in which the positions of the stent 2 coincide with each other are executed on two child windows on the monitor.

Alternatively, the system controller 21 controls the image processor 26 to display a region-of-interest designation screen to be used for designating one of the two stents as a region of interest. After any one of the stents is designated as the region of interest via the input unit 22, the system controller 21 controls the image processor 26 to perform processing only on the designated stent, as illustrated in FIG. 19B. For example, the system controller 21 controls the image processor 26 to generate only stent-fixed images in which the positions of the thus designated stent 1 coincide with each other. Therefore, even when medical treatment is being performed with a plurality of stents, the most appropriate stent-fixed images can be displayed as moving images in accordance with the distance between the stents. As described above, when a plurality of stents are used, the X-ray diagnostic apparatus 100 performs, with respect to each stent, the above-described control over the Learning mode.

Sixth Embodiment

Described in the above-described embodiments are cases where a coordinate point of a stent marker is detected with respect to each new image for generation of corrected images. In a case described in a sixth embodiment, a coordinate point of a stent marker is not detected with respect to a new image for generation of a corrected image. FIG. 20 is a diagram illustrating one example of the configuration of the image processor 26 according to the sixth embodiment. The image processor 26 according to the sixth embodiment is different from the image processor 26 illustrated in FIG. 3 in further including an electrocardiograph information acquisition unit 26 f, a periodic trace data acquisition unit 26 d, and a periodic trace data storage unit 26 e. The following description centers on this difference.

Here, in the sixth embodiment, as illustrated in FIG. 20, electrocardiographic equipment 28 that acquires an electrocardiographic waveform is attached to a subject P. The electrocardiograph information acquisition unit 26 f then acquires, from the electrocardiographic equipment 28, the electrocardiographic waveform of the subject P having a stent inserted therein. The electrocardiograph information acquisition unit 26 f can transfer an electrocardiographic waveform acquired from the electrocardiographic equipment 28 to each of the image data storage unit 25 and the periodic trace data acquisition unit 26 d. More specifically, as illustrated in FIG. 21, the X-ray diagnostic apparatus 100 according to the sixth embodiment generates X-ray images in a time-series manner with the X-ray tube 12 emitting X-rays and with the X-ray detector 16 detecting X-rays transmitted through the subject, as in the cases of the above-described embodiments, and, additionally, acquires cardiac phases of the subject P at the times of generation of X-ray images with the electrocardiograph information acquisition unit 26 f acquiring an electrocardiographic waveform from the electrocardiographic equipment 28 attached to the subject P. FIG. 21 is a diagram for explaining X-ray images according to the sixth embodiment.

Here, the X-ray diagnostic apparatus 100 in the sixth embodiment performs preliminary radiography for a predetermined period (for example, the duration of three heartbeats) starting from when display processing for images to be displayed is started. With this radiography, the image data storage unit 25 stores therein X-ray images corresponding to the duration of three heartbeats with cardiac phase information appended thereto, as preliminary images. A preliminary image refers to an image for collecting periodic trace data described later, and an image for use in diagnosis may be used as the preliminary image. Furthermore, an image obtained prior to the current radiography may be used as a preliminary image.

The marker coordinate detection unit 26 a according to the sixth embodiment then acquires a coordinate point of a stent marker with respect to each of the preliminary images. Next described with reference to FIGS. 22A and 22B is one example of processing that the marker coordinate detection unit 26 a according to the sixth embodiment performs on the preliminary images to detect the coordinate point of the stent marker. FIGS. 22A and 22B are diagrams for explaining the marker coordinate detection unit according to the sixth embodiment. First of all, when the preliminary images are stored in the image data storage unit 25, the system controller 21 performs control so that, for example, a plurality of preliminary images in a time-series manner that correspond to the duration of one heartbeat can be displayed on the monitor of the display unit 23. When these preliminary images are displayed, as illustrated in FIG. 22A, the system controller 21 performs control so that an operator can see what position (cardiac phase) in the electrocardiographic waveform each of the preliminary images has been generated at.

As illustrated in FIG. 22A, the operator then designates one position of a marker in, for example, one preliminary image corresponding to the end-systole, and further designates one position of the corresponding marker in another preliminary image corresponding to the end-diastole, from among the preliminary images displayed on the monitor. The following description assumes that, while a preliminary image at the timing of 30% in the interval between R waves (30% in the R-R interval) is designated as the preliminary image corresponding to the end-systole, a preliminary image at the timing of 70% in the interval between R waves (70% in the R-R interval) is designated as the preliminary image corresponding to the end-diastole.

The marker coordinate detection unit 26 a detects the coordinate points of the stent markers designated in the above-described two preliminary images, and defines rectangles centering on the coordinate points of the respective designated stent markers. As illustrated in FIG. 22B, the marker coordinate detection unit 26 a then extracts from the other preliminary images, for example, by use of a cross-correlation method, patterns that resemble patterns in the defined rectangles, and detects a coordinate point having the highest cross-correlation value as the coordinate point of the stent marker.

After the marker coordinate detection unit 26 a completes the processing, the system controller 21 may perform control so that a result of the processing performed on the preliminary images by the marker coordinate detection unit 26 a can be displayed on the monitor, to allow an operator to modify the coordinate points of the stent markers via a mouse of the input unit 22. As described in connection with the above-described embodiments, the marker coordinate detection unit 26 a may execute the processing by use of a teacher image also in this embodiment. Furthermore, the processing for detecting the coordinate points of the markers may be repeatedly executed on respective pluralities of preliminary images where each plurality of preliminary images correspond to one heartbeat, or may be executed on a plurality of preliminary images corresponding to three heartbeats at one time.

The periodic trace data acquisition unit 26 d then acquires periodic trace data of the stent marker in a time-series manner, based on: coordinate points of the stent marker detected in each plurality of preliminary images by the marker coordinate detection unit 26 a; and respective cardiac phases of the preliminary images at the times of generation of the preliminary images. Here, suppose that the operator selects, as a reference point, the coordinate point of the stent marker in the “preliminary image at 70% in the R-R interval” out of the two preliminary images in which the stent marker has been designated. In this case, as illustrated in FIG. 23A, the periodic trace data acquisition unit 26 d calculates, as a correction vector, the difference between a coordinate point of the stent marker detected in each of the preliminary images by the marker coordinate detection unit 26 a and the reference point in the “preliminary image at 70% in the R-R interval”.

Subsequently, the periodic trace data acquisition unit 26 d calculates an average correction vector with respect to each cardiac phase from correction vectors calculated for all of the preliminary images corresponding to the three heartbeats. For example, as illustrated in FIG. 23B, the periodic trace data acquisition unit 26 d calculates an average correction vector (vector C_(M)) at the “cardiac phase: M % in R-R interval” with respect to the reference point at the “cardiac phase: 70% in R-R interval”, thereby generating periodic trace data in which the cardiac phases are associated with the average correction vectors.

Back to FIG. 20, the periodic trace data storage unit 26 e stores the periodic trace data generated by the periodic trace data acquisition unit 26 d. This embodiment illustrates a case where the marker coordinate detection unit 26 a detects coordinate points only of the upper stent marker in the preliminary images, as illustrated in FIGS. 22A and 22B. However, the embodiment is not limited to this case, and the marker coordinate detection unit 26 a may detect coordinate points only of the lower stent marker in the preliminary images, or the marker coordinate detection unit 26 a may detect coordinate points of both of the stent markers.

When the periodic trace data is stored into the periodic trace data storage unit 26 e, the X-ray diagnostic apparatus 100 executes radiography/fluoroscopy of new images to be subjected to image processing, in accordance with an instruction of an operator. In this manner, as illustrated in FIG. 24, the image data storage unit 25 sequentially stores therein the new images to be subjected to image processing in association with cardiac phases estimated from an electrocardiographic waveform. FIG. 24 is a diagram for explaining new images in the sixth embodiment.

Back to FIG. 20, each time a new image is generated in a time-series manner, the corrected-image generation unit 26 b according to the sixth embodiment generates a corrected image from the new image, based on the periodic trace data stored in the periodic trace data storage unit 26 e and a cardiac phase at the time of generation of the new image. More specifically, as illustrated in FIG. 25, once a new image is stored, the corrected-image generation unit 26 b acquires from the periodic trace data an average correction vector corresponding to a cardiac phase at the time of generation of the new image, and generates a corrected image by using the acquired average correction vector.

As described above, in the sixth embodiment, corrected images and images to be displayed are generated from sequentially generated new images without the use of the marker coordinate detection unit 26 a. Therefore, this embodiment reduces a processing load on the image processor 26 to allow a reduction in processing time, thereby enabling more immediate display, of X-ray images as moving images with the visibility of a stent ensured.

Seventh Embodiment

A seventh embodiment describes, with reference to FIG. 26 and FIG. 27, a case where functions of the X-ray diagnostic apparatuses 100 according to the respective above-described embodiments are used in combination. FIG. 26 and FIG. 27 are diagrams for explaining the X-ray diagnostic apparatus 100 according to the seventh embodiment. The X-ray diagnostic apparatus 100 according to the seventh embodiment accepts, from an operator via the input unit 22, an instruction to execute either of the following modes explained in the above-described embodiments: the “real-time marker coordinate detection application mode” where processing for generating corrected images is executed by use of coordinate points of a stent marker detected in new images by the marker coordinate detection unit 26 a; and the “periodic trace data application mode” where processing for generating corrected images is executed by use of periodic trace data.

Here, when the marker coordinate detection unit 26 a has failed to extract a stent marker from a new image while the “real-time marker coordinate detection application mode” is running, the system controller 21 according to the seventh embodiment controls the corrected-image generation unit 26 b to generate corrected images after switching to the “periodic trace data application mode”. For example, as illustrated in FIG. 26, when a stent marker is not extractable at the k-th frame (cardiac phase: M % in the R-R interval), the corrected-image generation unit 26 b acquires a “vector C_(M)” from the periodic trace data under the control of the system controller 21. The “vector C_(M)” is a correction vector of the “cardiac phase at M % in the R-R interval” with respect to the reference point (at 70% in the R-R interval).

As illustrated in FIG. 26, while the “real-time marker coordinate detection application mode” is executed, the corrected-image generation unit 26 b then, from a coordinate point of the stent marker already detected by the marker coordinate detection unit 26 a from a new image generated at 70% in the R-R interval, estimates a coordinate point of the stent marker at the k-th frame by using the “vector C_(M)” as a correction vector to generate a corrected image.

On the other hand, also while the “periodic trace data application mode” is running, the system controller 21 according to the seventh embodiment performs control, using functions of the marker coordinate detection unit 26 a under the “real-time marker coordinate detection application mode”, so that the periodic trace data can be modified and updated. For example, as illustrated in FIG. 27, under the control of the system controller 21, the marker coordinate detection unit 26 a detects respective coordinate points of the stent marker from selected images, which have been selected from sequentially generated new images in such a manner that one frame is selected at every predetermined interval (for example, every five frames).

As illustrated in FIG. 27, under the control of the system controller 21, the periodic trace data acquisition unit 26 d then modifies and updates periodic trace data, which is stored in the periodic trace data storage unit 26 e, based on: respective coordinate points of the stent marker detected in selected images by the marker coordinate detection unit 26 a; and respective cardiac phases of the selected images at times of generation of the selected images. For example, under the control of the system controller 21, the periodic trace data acquisition unit 26 d modifies and updates the periodic trace data every 100 milliseconds. Subsequently, under the control of the system controller 21, the corrected-image generation unit 26 b executes processing for generating corrected images by using the updated periodic trace data stored in the periodic trace data storage unit 26 e.

As described above, in the seventh embodiment, corrected images can be generated by use of the periodic trace data when extraction of a coordinate point of a stent marker has failed, for example, because of image quality degradation of a new image while the “real-time marker coordinate detection application mode” is executed. The seventh embodiment thus makes it possible to continuously display X-ray images with a high visibility of a stent as moving images. Furthermore, in the seventh embodiment, the periodic trace data can be modified and updated by use of a detected coordinate point of a marker while the “periodic trace data application mode” is running. The seventh embodiment thus enables highly instantaneous image display, thereby making it possible to more reliably ensure the visibility of a stent in displayed X-ray images.

Note that whether to execute “the function of displaying as moving images X-ray images in which a stent appears stationary (hereinafter referred to as the present function)” explained in the above-described embodiments may be determined by an operator of the X-ray diagnostic apparatus 100 (a doctor or a technician). More specifically, with a button to select ON/OFF of the present function provided to the input unit 22 or near the couch, X-ray images in which a stent appears stationary can be displayed as moving images only when a doctor who performs treatment desires to display such X-ray images.

While the present function is in operation, a stent displayed on the monitor appears almost stationary. It is thus not needed to perform X-ray irradiation at a high rate in radiography/fluoroscopy that is executed while the present function is in operation. Therefore, the system controller 21 may perform the following control processing. More specifically, when the operation of the present function is started, the system controller 21 reduces an irradiation rate (for example, a pulse rate or a frame rate) for X-rays emitted from the X-ray tube 12, and returns the irradiation rate for X-rays to the original rate after operation of the present function is ended. For example, in cases of treatment of coronary arteries of the heart, the frame rate is normally about 15 to 30 frames/sec, and is reduced to, for example, half when the present function is in operation. The system controller 21 increases or decreases the irradiation rate for X-rays in accordance with a result of detection of a stent marker from the rate at the time when operation of the present function is started. Specifically, the system controller 21 increases again the irradiation rate for X-rays when detection of the stent marker has successively failed a predetermined number of times. In contrast, the system controller 21 further decreases the irradiation rate for X-rays when detection of the stent marker has been successful a predetermined number of times. This processing enables reduction in X-ray exposure.

Furthermore, for a stent having two stent markers attached thereto, processing described below may be additionally included at the time of generation of corrected images. More specifically, the corrected-image generation unit 26 b further correct corrected images by rotation based on positional information of the two stent markers so that the orientation of the stent visualized in the corrected images can be horizontal or vertical. This correction allows a doctor to more easily recognize, for example, the state of stent expansion because the doctor can view images that have the stent kept oriented horizontally or vertically.

In general, when performing endovascular intervention treatment, a doctor intermittently performs radiography/fluoroscopy. For example, a doctor performs radiography/fluoroscopy for 30 seconds, then stops radiography/fluoroscopy, and then restarts radiography/fluoroscopy 30 seconds later. Here, suppose that the radiography/fluoroscopy performed for the first 30-second period and the radiography/fluoroscopy performed subsequently are denoted as “A” and “B”, respectively, and “A” and “B” are performed independently and without correlation with each other. In such a case, it is highly likely that the angle of a stent appearing in stent-fixed images displayed during the radiography/fluoroscopy “A” is different from the angle (inclination) of a stent appearing in stent-fixed images displayed during the radiography/fluoroscopy “B”. For this reason, the stent is not clearly visible to a doctor when the doctor sees images displayed while the radiography/fluoroscopy “B” is running.

For this reason, on condition that “A” and “B” are performed at an interval within a predetermined time (for example, one minute), the corrected-image generation unit 26 b uses, during processing of “B”, information acquired during processing of “A” to perform processing for generating corrected images so that the angles of the displayed stents can be the same. Specifically, the corrected-image generation unit 26 b performs image deformation of X-ray images generated during the radiography/fluoroscopy “B” so that a stent marker therein may be positioned at a coordinate point of a stent marker extracted from X-ray images generated during the radiography/fluoroscopy “A”. With this image deformation, for example, when radiography/fluoroscopy is restarted within one minute, a doctor can observe a stent at the same angle (same inclination), and can continue manipulation without feeling odd. Note that this function is configured to be ON/OFF switchable and to enable a user to set the predetermined time (for example, one minute).

The above-described embodiments explain cases where image deformation is performed so that the positions of two stent markers in newly generated X-ray images can be set at the same positions as those of the two stent markers in an X-ray image at the first frame. However, the embodiments are not limited to this case, and may be a case where corrected images are generated by use of one point depending on two stent markers. More specifically, the marker coordinate detection unit 26 a performs processing of the Learning mode on one point depending on the two stent markers (for example, the midpoint between the two stent markers) to identify a position (a coordinate point), and detect, based on a result of the processing, one point depending on the stent markers in new images. The corrected-image generation unit 26 b generates corrected images, which have been corrected so that the one point depending on the stent markers that have been detected in each of the corrected images is set at the same point.

In such a case, the corrected-image generation unit 26 b uses one point and an angle determined from a feature pattern detected from an X-ray image (for example, the first frame) defined as a reference image. Based on feature patterns detected from target images, which are X-ray images to be corrected, a single predetermined point, and a predetermined angle, the corrected-image generation unit 26 b then generates corrected images from the target images. The system controller 21 then displays on the display unit 23, as moving images, corrected images sequentially generated by the corrected-image generation unit 26 b.

The following describes a case where a stent, which is a treatment tool, has two feature points (for example, two stent markers). In such a case, the marker coordinate detection unit 26 a detects, as the feature patterns, two feature points belonging to the tool. The corrected-image generation unit 26 b then uses, as the single predetermined point, one point determined depending on positions of the two feature points detected from the reference image. The corrected-image generation unit 26 b further uses, as the predetermined angle, an angle formed between a line segment connecting the two feature points detected from the reference image and a reference line in the reference image. FIG. 28 to FIG. 31 are diagrams for explaining the image processor 26 according to the seventh embodiment.

For example, the marker coordinate detection unit 26 a detects the two markers (M1 and M2) and positions (coordinate points) thereof from the X-ray image at the first frame, which has been defined as the reference image. For example, as illustrated in FIG. 28, the marker coordinate detection unit 26 a detects “(xs1, ys1) and (xs2, ys2)” as the positions of M1 and M2. Using the detection result from the marker coordinate detection unit 26 a, the corrected-image generation unit 26 b determines “one position (coordinate point)” for use in image deformation. For example, as illustrated in FIG. 28, the corrected-image generation unit 26 b calculates a central coordinate point “(xs, ys)” between M1 and M2. The central coordinate point is a midpoint of the line segment (hereinafter, the line segment M1&2) connecting M1 and M2. More specifically, “xs” is “(xs1+xs2)/2” and “ys” is “(ys1+ys2)/2”. Furthermore, for example, as illustrated in FIG. 28, the corrected-image generation unit 26 b calculates the angle “θs” formed between the line segment M1&2 and the reference line extending in the horizontal direction in the reference image.

Note that “(xs,ys)” and “θs” may be calculated by the system controller 21. An X-ray image to be used as the reference image may be an X-ray image at a frame other than the first frame (for example, the fifth frame). Otherwise, an X-ray image to be used as the reference image may be, for example, a first X-ray image since a cross-correlation value has become larger than a predetermined threshold. In the above-described manner, “the single point and the angle” to be used for image deformation processing are determined, and thereafter, the marker coordinate detection unit 26 a detects positions (coordinate points) of M1 and M2 in X-ray images to be corrected (target images) that have been generated after the reference image. Thereafter, as illustrated in FIG. 29, the corrected-image generation unit 26 b performs image deformation on the target images so that positions (coordinate points) of the midpoint of the line segment M1&2 in each of the target images can be (xs,ys) and that the angle between the line segment M1&2 and the reference line can be “θs”.

More specifically, in the seventh embodiment, image deformation is performed on target images so that a device visualized in corrected images can pass through a single point and that the device visualized in the corrected images can take the same angle (same inclination). The display control unit 21 c displays on the display unit 23, as moving images, corrected images sequentially generated by the corrected-image generation unit 26 b. In other words, display of moving images in the seventh embodiment is “single-point fixed display”, as illustrated in FIG. 29. The single-point fixed display is provided with enhanced visibility of a device as in the case of conventional two-point fixed display because the device is visualized at the substantially same point and at the same inclination.

However, in the single-point fixed display, while the orientation of a device and the direction of X-ray irradiation (a direction of X-ray radiography) is in a “diagonal relation”, when the degree of the “diagonal relation” changes, the distance (“Ls” in FIG. 28) between markers in the reference image fluctuate from one corrected image to another. More specifically, in the single-point fixed display, the distance between two markers may stretch and shorten centering on the white circle, which represents the central coordinate point (xs, ys), as illustrated in FIG. 30. In other words, in the single-point fixed display, not only the visibility of a device can be ensured, but also occurrence of “Foreshortening (a phenomenon where the length of a device appears shorter)” can be recognized. Specifically, the single-point fixed display enables recognition of occurrence of “Foreshortening in a state where the “diagonal relation” is being changed.

Additionally, as illustrated in FIG. 31, image deformation performed in the single-point fixed display is displacement processing that is either of translational displacement and rotational displacement, the sizes of objects located around the device do not change before and after the image deformation. In the single-point fixed display, therefore, even when body tissue around a device is used as an anatomical landmark during medical treatment, a doctor can easily determine a position of the device.

The above describes a case where the single point used for the single-point fixed display is the midpoint of the line segment M1&2 in the reference image. However, the single point used for the single-point fixed display may be M1 or M2 in the reference image. In such a case, for example, the corrected-image generation unit 26 b performs image deformation so that a position of M1 (or M2) detected from target images can be the same as the position of M1 (or M2) in the reference image.

Alternatively, the corrected-image generation unit 26 b may use a predefined point as the single point used for the single-point fixed display. For example, the corrected-image generation unit 26 b may use, as the single point used for the single-point fixed display, the central coordinate point of a region in which corrected images are displayed. In such a case, for example, the corrected-image generation unit 26 b performs image deformation so that positions of M1 detected in target images, positions of M2 detected in target images, or positions of the midpoint of the line segment M1&2 in target images can be located at the central coordinate point of a region in which corrected images are displayed. Conditions for setting the single point used in the above-described single-point fixed display may be changed to those desired by an operator of the X-ray diagnostic apparatus.

Additionally, “the function of displaying as moving images X-ray images in which a stent appears stationary” explained in the above-described embodiments may be applied to processing executed on a real-time basis at the same time as X-ray irradiation, and may be applied to processing executed on X-ray images generated in a time-series manner in the past.

Furthermore, as medical treatment that is performed with reference to X-ray images, endovascular intervention treatment is illustrated as a case where a stent is used as a medical treatment tool. The present embodiments are not limited to this case, and are applicable to medical treatment tools for use in various kinds of medical treatment that is performed with reference to X-ray images.

Techniques according to the embodiments are applicable to, for example, treatment with the use of any of the following treatment devices by using the device as a marker: an electrode of an electrophysiological catheter for arrhythmia treatment; a Rotablator drill for treating a hard stricture site that is difficult to expand with a balloon or a stent; a holed metal cylinder attached on a tip end of a catheter for directional coronary atherectomy; and a catheter with an ultrasonic-wave transmitting-receiving function for checking conditions inside a blood vessel of a stricture site. Examples of treatment devices include: an angioscope; a vascular ultrasound device; a vascular magnetic resonance imaging (MRI) device; an optical coherence tomography (OCT) device; a device for implanting stem cells in the regenerative medicine field; an artificial valve; and a vascular graft. Furthermore, techniques according to the present embodiments can be applied to various clinical practices such as: hybrid treatment involving both a surgical aspect and an internal medicine aspect; and guidance on needling for biopsy in a surgical treatment.

As described above, at least one of the embodiments enables a reduction in radiation exposure.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

What is claimed is:
 1. An X-ray diagnostic apparatus comprising: processing circuitry configured to successively generate a plurality of X-ray images based on X-rays emitted from an X-ray tube and transmitted through a subject, detect a position of a target in each of the plurality of X-ray images, identify a first region that is stationary among the plurality of X-ray images and that includes all the positions of the detected target in each of the plurality of X-ray images, the first region being a region in which the target is visible throughout the plurality of X-ray images, perform control to reduce an X-ray irradiation dose to a second region that excludes the first region, acquire an X-ray image which the X-ray irradiation dose to the second region is reduced, extract a first period having an amount of change in the position of the target that is smaller than a threshold and is periodically repeated in a period for successively generating the plurality of X-ray images, and alternately switch between a first frame rate in the first period and a second frame rate in a second period that excludes the first period by controlling the first frame rate to be lower than the second frame rate.
 2. The X-ray diagnostic apparatus according to claim 1, wherein the processing circuitry is configured to perform the identifying of the first region by identifying third regions that are non-stationary regions that respectively include the detected target in each corresponding X-ray image of the plurality of X-ray images, and determining the first region to be a stationary region among the plurality of X-ray images that covers each of the third regions.
 3. The X-ray diagnostic apparatus according to claim 1, wherein the processing circuitry is further configured to control image processing on the first region, and perform the control to reduce the X-ray irradiation dose to the first region, based on the image processing on the first region.
 4. The X-ray diagnostic apparatus according to claim 1, wherein, the processing circuitry is configured to alternately change the number of X-ray images to be generated per unit time for the period for successively generating the plurality of X-ray images based on the first frame rate and the second frame rate.
 5. The X-ray diagnostic apparatus according to claim 1, wherein, based on heartbeats of the subject, the processing circuitry is configured to extract the first period.
 6. The X-ray diagnostic apparatus according to claim 1, wherein the processing circuitry is configured to reduce the X-ray irradiation dose to the second region by inserting an X-ray collimator or an X-ray absorption filter into the second region.
 7. The X-ray diagnostic apparatus according to claim 1, wherein the processing circuitry is further configured to successively generate corrected images obtained by subjecting newly generated X-ray images to correction processing to cause a position of the target detected in the newly generated X-ray images to coincide with a reference position that is a position of the target detected in a reference image.
 8. The X-ray diagnostic apparatus according to claim 1, wherein the processing circuitry is configured to perform the identifying of the first region by detecting positions of a plurality of targets in each of the plurality of X-ray images, identifying in each of the plurality of X-ray images a respective third region including a corresponding detected target of the plurality of detected targets, the respective third regions being non-stationary among the plurality of X-ray images, determining the first region to be a stationary region among the plurality of X-ray images that covers each of the respective third regions.
 9. The X-ray diagnostic apparatus according to claim 1, wherein the target is a stent marker.
 10. The X-ray diagnostic apparatus according to claim 1, wherein the processing circuitry is configured to execute high-frequency noise reduction filtering on the X-ray image based on X-rays with the reduced irradiation dose, by using an image filter.
 11. The X-ray diagnostic apparatus according to claim 1, wherein, when a enlarging operation is executed on an X-ray image displayed at a present time, the processing circuitry is configured to control an imaging system so that all the positions of the detected target in each of the plurality of X-ray images are included in an enlarged region.
 12. The X-ray diagnostic apparatus according to claim 2, wherein the processing circuitry is further configured to control image processing on the third regions, and perform the control to reduce the X-ray irradiation dose to the first region, based on the image processing on the third regions.
 13. The X-ray diagnostic apparatus according to claim 4, wherein, based on heartbeats of the subject, the processing circuitry is configured to extract the first period. 